Sparingly water-soluble active ingredients such as glycyrrhetinic acid and tocopherols can impart various pharmacological actions and therefore have been conventionally widely used as medicinal ingredients. For example, Patent Literature 1 discloses a dentifrice composition exhibiting excellent medicinal effects and having enhanced persistence thereof by containing a sparingly water-soluble active ingredient such as tocopherols and an oily ingredient, as well as a sucrose fatty acid ester and an anionic surfactant each at a specific mass ratio. Patent Literature 2 discloses a dentifrice composition containing a specific amount of a specific peppermint oil together with the above-mentioned active ingredient and surfactant so as to express good flavor in addition to the excellent medicinal effects.
Incidentally, the main component of dentin is hydroxyapatite. In the mouth, elution (decalcification) of phosphate ions and calcium ions and crystallization (remineralization) to calcium phosphate and hydroxyapatite are generally in equilibrium; and dental caries is developed by acceleration of decalcification through decomposition of, for example, sucrose by bacteria such as Streptococcus mutans to generate organic acids, lower the pH, and elute calcium and others from the tooth. In the early stage of dental caries, a subsurface decalcification lesion called a white spot, occurs on the enamel. Here, fluoride ions, which accelerate crystallization of calcium ions and phosphate ions, i.e., remineralization to prevent occurrence of dental caries and can extinguish such white spots, are known to be useful.
Accordingly, water-soluble active ingredients such as sodium fluoride, which can supply fluoride ions to teeth in the oral cavity, are also widely used as medicinal ingredients. For example, Patent Literature 3 discloses a technique for improving the retentivity of fluorine on tooth surfaces by mixing specific amounts of fatty acid amide propyl betaine, carrageenan, and a cellulose derivative such as hydroxyethyl cellulose, while containing sodium fluoride. Patent Literature 4 discloses a technique for improving adsorption of fluoride ions to teeth by using a fluoride ion-supplying compound such as sodium fluoride, an N-acylamino acid salt, and a specific sugar alcohol.    (Patent Literature 1) JP-A-2005-289917    (Patent Literature 2) JP-A-2007-45786    (Patent Literature 3) JP-A-2009-155217    (Patent Literature 4) JP-A-2014-125443